Great insideline track test preview of performance model S

[DSA]

Right then, I'll challenge you to 10 laps at 90 degrees F. See which car goes around faster. It'll be the Model S, because the Roadster will be at 1/4 power limit due to motor overheating.

True enough. But what about the first lap out of those ten laps? :wink: The Refuel Races we've had the last few years here in California, for example, are based on a one lap time trial, where there would be hope for the Roadster getting in a good time before becoming power limited. During the races last month, the Model S's didn't degrade in performance due to heating as much as the Roadsters over successive laps. I'd love to see exactly how improved the Model S is in terms of cooling - exactly how much does the Model S become current limited over the course of hard driving?

I've got some pretty good data for the Roadster - posted on the Refuel Races thread. It was a pretty clear and dramatic drop in power over the course of 15 minutes of hard driving on the track - current available to the motor started at 515 Amps available and dropped to only 30% of that, about 150 Amps. How much power (or current) was still available for the Model S's after 15 minutes on the track? The ones I was following did seem to get slower over the course of hard driving, but I'm not exactly holding my breath waiting for Tesla to release vehicle logs from those runs. I guess once some spirited Model S drivers get in some track time, maybe we'll get some data.

By the way, it seems pretty easy at this point to get useful data out of the Roadster vehicle log, with a big thank you to those who have created tools to mine the data. Can Model S owners also plug in a usb stick and download logs from the Model S? (sorry if this is off-topic, I can post elsewhere if needed)

 

[Doug_G]

I had my Roadster out to Shannonville Motorsports recently (along with 4 others), and after 3 hot laps it backed down the power to about half. After another couple of laps it backed off even more, and I headed to the pits. Loads of fun while it lasted!

It depends on the abient temperature of course. We've had a very hot summer here, and that day was fairly hot.

 

[DSA]

Loads of fun while it lasted!

Yup. I felt the same at Laguna Seca - performance backed off after a few laps, but what a blast while it lasted. All of the performance numbers and such are great to compare, but I think it comes down to the fact that Tesla is putting out some really fun to drive cars with the Roadster and Model S. I just had one of those "oh, the light changed to yellow but I can floor it and still make it!" <floor the pedal, no shifting required, watch the entire world blur as the acceleration kicks in> moments earlier today in the Roadster. What a blast. I'm sure many folks will have similar experiences in the Model S. I can't wait to test drive a Model S myself. I'm not a reservation holder, but some day they should be more available for test drives.

 

[chrisn]

Dropping from 4.3 to 4.6 seconds after several runs suggests about a 10% drop in power, which is significant. Has anyone put an MSP on a dyno and done multiple pulls?

Skidpad numbers look really bad (same as my Acura MDX). Something fishy there. I would wait for another full test before drawing any conclusions.

 

[stopcrazypp]

Dropping from 4.3 to 4.6 seconds after several runs suggests about a 10% drop in power, which is significant. Has anyone put an MSP on a dyno and done multiple pulls?

Skidpad numbers look really bad (same as my Acura MDX). Something fishy there. I would wait for another full test before drawing any conclusions.

The skidpad for the MDX is 0.84, so the Model S is not quite as bad at 0.86, although it really should be higher (esp. given the huge gap in the slalom speeds).
http://blogs.insideline.com/straightline/2010/03/il-track-tested-2010-acura-mdx.html

I think CapitalistOppressor probably nailed the reason. The Model S doesn't have an ICE and it changes the way to get a max skidpad number (the TC might also have to do with it).

 

[Doug_G]

Dropping from 4.3 to 4.6 seconds after several runs suggests about a 10% drop in power, which is significant. Has anyone put an MSP on a dyno and done multiple pulls?

Perhaps, but insignificant compared to the power loss in the Roadster. After six laps in hot weather it was slower than a Miata.

 

[CapitalistOppressor]

My background is in drag racing rather than twisty racing, but it's actually easier to see the rotational effects of an ICE engine at the drag races. High powered cars lift up the front end on launch but they also twist the front of the car with one wheel significantly higher than the other.

On street cars with an engine that isn't mounted sideways you should be able to rev the engine and actually cause one of your front wheels to press more firmly against the ground and allow greater turning force. I think they run the skid pad test in both directions to help smooth out this effect, but in either direction you can get an advantage by modulating the throttle.

Model S has a tiny sideways mounted motor located in the rear axle. It loses out on all of the advantageous physics available on an ICE in this type of test. Even the front end being lighter is probably a problem in a high acceleration turn. If TC was off you could break MSP loose and take advantage of the 50/50 weight distribution and low Cg to point the car where you want to go and the accelerate to get there faster.

 

[CapitalistOppressor]

Here are examples of the rotational force of an ICE engine biasing one of the front corners of a car. In a skidpad type test with an ICE engine mounted inline one of the front tires is forced down against the pavement, with more force generated the higher you rev the engine.

So putting the car in low gear and accelerating at high RPM basically allows you to plant an anchor at one of the front corners to help rotate the car around. You can modulate the throttle to increase or decrease this effect while going around in a circle and get better performance.

The energy gets built up in the chassis which can be released (by lowering the throttle) to generate extra turning acceleration as well so when you are about to roll over your tires and start moving sideways you can lower the throttle and actually get extra (controlled) acceleration in the direction you want. I think because of this drivers constantly adjust the throttle up and down on the skidpad to balance these forces and get the best results. Certainly thats how Gran Turismo tells me to modulate the throttle along with micro-braking during the skidpad portion of the licensing tests so I can get the gold star instead of just the bronze

MSP just doesn't work this way, which is why I think in a race you'd really want to defeat the traction control to accelerate in controlled drifts around a turn, which the opposite of what you are trying to accomplish on a skidpad test. That way you take advantage of your superior weight distribution and super low Cg.

Roadster likely gets good skidpad numbers because its just so light that its tires retain grip despite its disadvantages.

Again, here are the test notes from Edmunds -

Definitely felt the weight here, and the lack of a free-revving internal combustion engine means changes in throttle have less effect on the chassis. Still, car felt pretty precise.

 

[Brian H]

...
If the rumours of a huge motor upgrade in the works for the Roadster are true, one of the things they probably did was make it liquid cooled-- maybe even shoehorned in the Model S motor, as they did with the new RAV4 EV.

Ya, I've seen that stated explicitly, somewhere. Also, in a recent interview Elon said building the Roadster on the Elise chassis was a serious mistake; like reno'ing a house and ending up with one original wall in the basement, and all the rest revised. So a clean-sheet Roadster will be radically better.

 

[Krugerrand]

Perhaps, but insignificant compared to the power loss in the Roadster. After six laps in hot weather it was slower than a Miata.

Hey! Miata's need loving too.

 

[brianman]

in a recent interview Elon said building the Roadster on the Elise chassis was a serious mistake; like reno'ing a house and ending up with one original wall in the basement, and all the rest revised. So a clean-sheet Roadster will be radically better.

Do you have a link? I would expect Elon to describe the other options that were available at the time, and the Tesla back story here sounds interesting.

 

[goyogi]

Do you have a link? I would expect Elon to describe the other options that were available at the time, and the Tesla back story here sounds interesting.

Q and A: Elon Musk, CEO, Tesla - Automobile Magazine


"As it turned out, the AC Propulsion technology didn't work, so we had to redo all that. And the Elise -- once you added the electric powertrain, it invalidated all the crash work, the mass grew by 30 percent, the weight distribution was different, the load points were all different. We had to stretch the chassis just to be able to fit people in, so that turned out to be a really dumb strategy, too.

So it was like you wanted to build a house, couldn't find the right house, so you try to fix an existing house and end up changing everything except for one wall in the basement. It would have cost way less to just level the house [laughs] and start from scratch. What sounded like a good idea at first, which was to leverage the Elise chassis, was actually an incredibly dumb idea [laughs]."

 

[Doug_G]

Hey! Miata's need loving too.

He he he. Yeah, Miatas are actually pretty decent track cars, especially if they've been modded. It's a lot of fun pulling a Miata owner's leg, though, because they're always just a little sensitive. :tongue::biggrin: